Overview

Herpes simplex encephalitis is a severe viral infection of the central nervous system. Herpes simplex encephalitis may be classified according to origin of disease into two subtypes: oral (HSV-1) and genital (HSV-2). The exact pathogenesis of herpes simplex encephalitis is not fully understood.[1] Herpes simplex encephalitis must be differentiated from other diseases that cause fever, headache, and altered mental status. Physical examination findings for herpes simplex encephalitis are generally unspecific. Herpes simplex encephalitis constitutes a medical emergency. If left untreated, approximately 70% patients with herpes simplex encephalitis progress to mortality.[2] Common complications of herpes simplex encephalitis include meningitis, increased intracranial pressure, and coma. Laboratory findings consistent with the diagnosis of herpes simplex encephalitis include increased leukocytes in cerebrospinal fluid.[3]Polymerase chain reaction is critical in the diagnosis of herpes simplex encephalitis, as there is a 95-98% specificity and sensitivity beginning as early as one day after symptoms first appear and lasting up to one week after treatment.[1]Magnetic resonance imaging is the imaging modality of choice for herpes simplex encephalitis. The mainstay of therapy for herpes simplex encephalitis includes antiviral therapy. The drug of choice is acyclovir.[4]

Classification

Herpes simplex encephalitis may be classified according to origin of disease into two subtypes: oral (HSV-1) and genital (HSV-2).

Epidemiology and Demographics

Incidence

The incidence of herpes simplex encephalitis is approximately 0.1-0.2 per 100,000 individuals worldwide.[2][6] Approximately 2,000 cases of herpes simplex encephalitis occur within the United States annually.[4] Approximately 90% of cases are caused by HSV-1, with 10% caused by HSV-2. HSV-2 infection is most commonly observed among immunocompromised individuals and neonates.

Age

Approximately 50% of individuals who develop herpes simplex encephalitis are over 50 years of age.[3]

Gender

There is no gender predilection to the development of herpes simplex encephalitis.[4]

Race

There is no racial predilection to the development of herpes simplex encephalitis.[4]

Season

Unlike other cases of encephalitis, there is no seasonal predilection to the development of herpes simplex encephalitis.[4]

Risk Factors

The most potent risk factor in the development of herpes simplex encephalitis is immune deficiency. Other risk factors include age and extent of human contact.[4][20]

Natural History, Complications and Prognosis

Natural History

Herpes simplex encephalitis constitutes a medical emergency. If left untreated, approximately 70% patients with herpes simplex encephalitis progress to mortality.[2]

Complications

Prognosis

The prognosis for herpes simplex encephalitis is generally poor. Even with rapid treatment, it is fatal in approximately 20% of cases. In approximately 50% of surviving patients, long-term neurological damage is present. Only 2.5% of survivors regain full brain function.[3]

Diagnosis

Diagnostic Criteria

The diagnosis of herpes simplex encephalitis is based on the IDSA criteria, which can be found here.[21]

History and Symptoms

If possible, a detailed and thorough history from the patient is necessary. Symptoms of herpes simplex encephalitis include:[4]

Laboratory Findings

Laboratory findings consistent with the diagnosis of herpes simplex encephalitis include increased leukocytes in cerebrospinal fluid obtained via lumbar puncture.[3]Polymerase chain reaction is critical in the diagnosis of herpes simplex encephalitis, as there is a 95-98% specificity and sensitivity beginning as early as one day after symptoms first appear and lasting up to one week after treatment.[1]

Primary Prevention

Effective measures for the primary prevention of herpes simplex encephalitis include abstinence from sexual contact, remaining in a long-term mutually monogamous relationship with an uninfected partner, use of latex condoms, and conversing with possible sexual partners regarding infections. Vaccines against herpes simplex have been developed but remain experimental.